1. Field of The Invention
The invention relates to a card edge connector, and particularly to contact arrangement thereof so as to meet the requirements of high speed transmission.
2. The Related Art
DIMM (Dual In-line Memory Module) connectors are now popularly used in the personal computers. The typical DIMM connector is of substantially a card edge connector with two ejectors at two opposite ends thereof. The most common type contact used in the DIMM connector is of a single beam type as shown in U.S. Pat. No. 5,470,242 in which the contact is deflectably engaged with the corresponding circuit pad on the inserted module.
Generally speaking, this arrangement is okay for the traditional card edge or DIMM connector. While recently, the high speed transmission is required in the personal computer, and thus such style contact is no longer acceptable in that situation because of the inductance of the contact being regarded too high. Therefore, how to lower the inductance of the contact is a key thing for the high speed connector.
Basically, increasing the cross-section area of the contact to reduce the electrical resistance is an ideal way to lower the corresponding inductance thereof. While oppositely, increasing the cross-section area also increases the spring constant K of the contact from a mechanical viewpoint, thus improperly increasing the undesired insertion force between the inserted module and the corresponding contact.
Anyhow, in an earlier years there were some other type contacts of the so-called PLCC connectors wherein each contact generally included a moveable arm and an immovable arm wherein the moveable arm was adapted to be deflected and slidably engaged with the immovable arm so as to attain a shorter signal path through the immovable arm while still owning thereof superior mechanical resiliency substantially provided by the moveable arm for mechanical and electrical engagement with the electrical component embedded within the connector socket. Under that situation, those two moveable and immovable arms can be deemed as in a parallel relationship from an electrical viewpoint, and thus the integral inductance L of the contact can be lowered in comparison with the single moveable arm arrangement, with reference to Equation: 1/Lt(total) is equal to 1/Lm(moveable arm) plus 1/Li(immoveable arm), for example, U.S. Pat. Nos. 4,354,729, 4,504,887 and 4,684,184.
Nevertheless, such an arrangement can not be directly applied to the card edge connector, which requires a low insertion force of the inserted module, because of the high insertion force derived from the immovable arm.
Therefore, an object of the invention is to provide a card edge connector for use with high speed transmission wherein the contact arrangement in the connector can achieve not only a lower inductance thereof but also a lower insertion force, both of which are required in the high speed connector.